Methods and devices for verifying the authenticity of sheet-type products

ABSTRACT

Ultraviolet light is used for checking the authenticity of sheet material, in particular bank notes, whereby the ultraviolet light transmitted, i.e. pervading the sheet material to be checked, is used for checking authenticity.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a National Phase of International Application No.PCT/EP02/13941, filed Dec. 9, 2002.

FIELD OF THE INVENTION

The present invention relates to methods and apparatuses for checkingthe authenticity of sheet material, in particular bank notes, by meansof ultraviolet light.

DESCRIPTION OF THE BACKGROUND ART

Methods and apparatuses for checking the authenticity of sheet material,in particular bank notes, by means of ultraviolet light are known fromU.S. Pat. No. 5,640,463 or U.S. Pat. No. 5,960,103, for example. Knownmethods and apparatuses are based on the finding that the paper used forbank notes has special properties because it is produced from cotton, onthe one hand, and contains no optical brighteners, on the other hand.Upon irradiation with ultraviolet light there is thus no fluorescenceeffect, i.e. short-wave, ultraviolet light is not converted tolonger-wave, visible light. Moreover, a relatively great portion ofultraviolet light is reflected by the surface of the bank note to beevaluated. Forgeries can therefore be recognized if they are irradiatedwith ultraviolet light for evaluation and the optical brightenersthereby result in longer-wave, visible light. With certain forgeries ithas turned out, however, that there is no conversion of short-wave,ultraviolet light to longer-wave, visible light. In these cases aforgery can be recognized, however, when the ultraviolet light reflectedby the forgery is examined. If the amount of reflected ultraviolet lightshould fall below a first, lower threshold value or exceed a second,upper threshold value, a forgery is likewise present, since the amountof reflected ultraviolet light is normally only within a certain rangewith authentic bank notes.

Known methods and apparatuses for checking the authenticity of sheetmaterial, in particular bank notes, by means of ultraviolet light havethe disadvantage, however, that forgeries cannot be recognized if theyhave no fluorescence effect and the evaluation of the amount ofreflected ultraviolet light also fails to yield a clear statement.

SUMMARY OF THE INVENTION

The problem of the present invention is therefore to specify methods andapparatuses for checking the authenticity of sheet material, inparticular bank notes, by means of ultraviolet light which permit a morereliable distinction between forgeries and authentic bank notes.

In a first consideration, the invention starts out from the use ofultraviolet light for checking the authenticity of sheet material, inparticular bank notes, whereby the ultraviolet light transmitted, i.e.permeating the sheet material to be checked, is used for checkingauthenticity.

The advantage of the invention is in particular to be seen in the factthat, departing from methods and apparatuses known from the prior art,not only the surface of the sheet material to be checked which isexposed to the ultraviolet light used for the check, but rather thetotal material, i.e. the total thickness, of the sheet material to beexamined interacts with the ultraviolet light. The effects on theultraviolet light used for the check are therefore considerably morepronounced, so that the check of the ultraviolet light transmitted bythe sheet material permits forgeries to be recognized even in caseswhich were hitherto not distinguishable from authentic sheet material,since the differences in the quantities of transmitted ultraviolet lightare considerably more pronounced between forgeries and authentic sheetmaterial.

In a second consideration, the invention likewise starts out from theuse of ultraviolet light for checking the authenticity of sheetmaterial, in particular bank notes, whereby the ultraviolet lighttransmitted, i.e. permeating the sheet material to be checked, is usedfor checking authenticity. In addition to the ultraviolet light,however, at least one further light of a different wavelength is used,whereby the further light transmitted, i.e. permeating the sheetmaterial to be checked, is likewise used for checking authenticity, forwhich purpose the transmitted ultraviolet light and the transmittedfurther light are set in a mutual relation.

The advantage of the invention according to the second consideration isin particular to be seen in the fact that, departing from methods andapparatuses known from the prior art, the check can be done almostindependently of any soiling of the sheet material to be examined, sincethe effects arising from soiling on the light passing through the sheetmaterial are the same or have a defined relation for both theultraviolet light and the further light. When the transmittedultraviolet light and the transmitted further light are set in a mutualrelation, the effects due to soiling cancel out.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages of the present invention will result from thedependent claims as well as the following description of embodimentswith reference to figures, in which:

FIG. 1 shows a first embodiment of an apparatus for checking theauthenticity of sheet material by means of ultraviolet light, and

FIG. 2 shows a second embodiment of an apparatus for checking theauthenticity of sheet material by means of ultraviolet light.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a first embodiment of an apparatus for checking theauthenticity of sheet material, in particular bank notes, by means ofultraviolet light. In the following description it will be assumed thatthe sheet material is bank notes. The bank notes BN are transported by atransport system (not shown) in a transport direction T past a sensor 20and a light source 21. It is possible that the bank notes BN aretransported along their long side or along their short side. The lightsource 21 produces light which is suitable for checking the authenticityof the bank notes BN and is in the ultraviolet range, i.e. has awavelength below 400 nm. The light source 21 can produce the ultravioletlight directly, or a filter 23 passing only ultraviolet light can beprovided. The ultraviolet light permeates the bank note BN at a place 15which sweeps over the total length or width (depending on the selectedtype of transport) of the bank note BN during transport of the bank noteBN in the transport direction T. The transmitted ultraviolet light isdetected by the sensor 20. The sensor 20 can be sensitive only to theultraviolet light produced by the light source 21, or a filter 22 onlypassing corresponding ultraviolet light to the sensor 20 can beprovided. The light source 21 used can be for example one or more UVlight-emitting diodes. It is equally possible to use for example one ormore fluorescent tubes producing ultraviolet light. At the place of thefilters 22 and 23, further optical systems such as lenses can beprovided in addition to or instead of the filters 22 and 23 to obtainfor example a special focusing at the place 15 or at the sensor 20.

To check the authenticity of the bank notes BN, the light source 21emits ultraviolet light with a wavelength under 400 nm. Since duringtransmission of the ultraviolet light through the bank note BN most ofthe ultraviolet light is absorbed in the material of the bank note BN,there was hitherto no attempt to use the measurement of the ultravioletlight transmitted by the bank note BN as a criterion for checking theauthenticity of the bank note BN. It was noticed, however,that—precisely because of the great influence on the ultraviolet lightwhen passing through the bank note BN, i.e. because of the greatabsorption that occurs—the evaluation of the transmitted ultravioletlight has particularly good informative power about the material of theparticular bank note BN checked and thus about its authenticity.

Despite the small quantity of ultraviolet light available aftertransmission on the side of the sensor 21, better distinction betweenauthentic bank notes BN and forgeries is possible since the relativedifferences between authentic bank notes BN and forgeries are verygreat.

Forgeries made of normal paper without an optical brightener, i.e. paperproduced from wood, have the best permeability to ultraviolet light. Ifthe forgeries consist of paper produced from cotton like authentic banknotes, the forgeries have poor permeability to ultraviolet light, sincesuch paper as a rule contains added substances which absorb theultraviolet light to imitate the lack of brightener known in authenticbank notes.

Therefore, bank notes BN can be distinguished reliably from forgeries ifthe quantity of transmitted ultraviolet light detected by the sensor 20is above a lower threshold value and below an upper threshold value. Ifthe sensor 20 detects a quantity of ultraviolet light which is above theupper threshold value, a forgery made of normal paper (wood) is present,while if the quantity of ultraviolet light detected by the sensor 20 isbelow the lower threshold value, a forgery made of bank note paper(cotton) is present.

Since the effect on the ultraviolet light is particularly great in caseof transmission, as described above, forgeries can be reliablydistinguished from authentic bank notes since the threshold values usedare very far apart. The described effects occur for bank notes from allcurrencies examined hitherto; any deviations can be compensated by asuitable choice of threshold values.

For evaluating the quantities of transmitted ultraviolet lightdetermined by the sensor 20, an evaluation unit 10 with a connectedmemory 11 is provided. The evaluation unit 10 can be formed for exampleby a microprocessor with a connected memory 11, whereby the memory 11can have a volatile and a nonvolatile area. The nonvolatile area of thememory 11 stores in particular the above-mentioned threshold values. Topermit the measurements from the sensor 20 to be processed by theevaluation unit 10, an analog/digital converter is provided for examplein the sensor 20 for converting the analog output signal of the sensor20 to a digital value.

The evaluation unit 10 compares the values from the sensor 20 with thethreshold values, thereby checking the authenticity of the bank note BN.Depending on the result of the check, the evaluation unit 10 identifiesthe bank note BN as authentic or as a forgery. This identification canbe used for the further processing of the bank note BN, e.g. to controlthe above-mentioned transport system, thereby making it possible toseparate forgeries from authentic bank notes. For this purpose theforgeries are transported to a special output pocket, for example.

For evaluation of the values of the sensor 20 by the evaluation unit 10there are different procedures that can be used. For example, an averagecan be produced by the evaluation unit 10 from all the values producedwhile the bank note BN is transported past the sensor 20, and saidaverage compared with the threshold values. It is equally possible todetermine at least one pattern for the bank notes to be checked and tostore it in the memory 11. In this case the values produced while thebank note BN is transported past the sensor 20 are checked for agreementwith the pattern to determine the authenticity of the bank note BN. Afurther possibility is to examine only certain areas of the bank noteBN, e.g. areas without printing, and to compare them with thresholdvalues.

A further improvement in authenticity testing can be obtained if afurther sensor 30 which can detect light in the visible range, i.e. witha wavelength greater than 400 nm, is provided on the side of the lightsource 21. If the sensor 30 should also be able to detect light with asmaller wavelength, a filter 32 not permeable to these light componentscan be provided. If a forgery containing an optical brightener ispresent, the ultraviolet light of the light source 21 is converted by afluorescence effect to visible light which is detected by the sensor 30.To permit the signal of the sensor 30 to be processed by the evaluationunit 10, the sensor 30 contains an analog/digital converter whichconverts the sensor signal to a digital value. If the digital valueexceeds a predetermined threshold value for brightener measurement whichis stored in the memory 11, a forgery is recognized by the evaluationunit 10.

FIG. 2 shows a second embodiment of an apparatus for checking theauthenticity of sheet material, in particular bank notes, by means ofultraviolet light. The second embodiment according to FIG. 2 is built upessentially like the first embodiment according to FIG. 1. The functionof the apparatus according to the second embodiment likewise correspondsessentially to the function of the apparatus according to the firstembodiment. However, the apparatus additionally has on the side of thesensor 20 for ultraviolet light a second light source 31 which produceslight in a visible range, i.e. with a wavelength greater than 400 nm.Should the second light source 31 have shorter-wave components, a filter33 can be provided which does not pass them.

As described above in connection with FIG. 1, the first light source 21and the first sensor 20 serve the purpose of checking the authenticityof bank notes by means of transmitted, ultraviolet light. The secondsensor 30 which detects light in the visible range and is disposed onthe side of the first light source 21 producing ultraviolet light servesthe purpose—as described—of detecting the presence of opticalbrighteners.

Additionally the second sensor 30 is used for detecting the transmittedlight of the second light source 31 for visible light. If a forgery withoptical brightener contained in the paper is present, the fluorescenceeffect produces a relatively large amount of visible light so that theabove-described threshold value for brightener measurement is exceeded.If the fluorescence effect does not occur, only a considerably smalleramount of visible light is present which is below the threshold valuefor brightener measurement. This light is from the second light source31 and was transmitted by the bank note BN. From the second sensor 30the corresponding values which are digitized by an analog/digitalconverter are passed to the evaluation unit 10 and set by the evaluationunit 10 in a relation with the values of the first sensor 20, e.g. bydivision of the values of the first sensor 20 by the values of thesecond sensor 30. Before the division of the values or instead of thedivision, a special correction of another mathematical relation can alsobe effected, which results from the same kind of influence on thevisible light and the ultraviolet light.

This procedure permits compensation of any soiling of the bank notes BNto be checked, since the above-described effects on the light upontransmission by the bank note are not changed by soiling. Soilinginstead causes a reduction of the transmitted light quantity, both forthe light of the first light source 21 and for the light of the secondlight source 31. The soiling of bank notes can therefore be compensatedif the values of the first sensor 20 are set in a relation with thevalues of the second sensor 30, as described. Suitable threshold valuesor patterns must in this case of course be provided for the check andstored in the memory 11. The threshold values are obtained by means ofauthentic bank notes by setting values of the first sensor 20 in arelation with values of the second sensor 30.

Since the soiling of the bank notes can have strong local fluctuations,it has proved especially expedient that first and second sensors 20 and30 evaluate the bank note BN at the same place 15.

Ideally, the wavelength of the second light source 31 is chosen—asdescribed—so that the second sensor 30 already present for detectingoptical brighteners can be used for detecting the transmitted light, forexample in such a way that the light is in the blue range. It is equallypossible to choose another wavelength to compensate soiling effects,however. In particular, the wavelength of the second light source 31 andthe second sensor 30 can also be smaller than the wavelength of thefirst light source 21 and the first sensor 20. In this case, however, afurther sensor (not shown) must be provided on the side of the firstlight source 21 to permit a check of the presence of opticalbrighteners.

To compensate effects like aging, soiling or temperature fluctuationswhich affect the sensors 20, 30 or the light sources 21, 31, it can beprovided that a calibration is carried out in the gaps between banknotes BN to be checked. Reference values stored in the memory 11 arethus compared by the evaluation unit 10 with the values of the sensors20, 30. If deviations appear, the evaluation unit 10 can readjust thelight sources 21, 31 for example. Calibration can also be carried out bymeans of separate monitor receivers (not shown), i.e. sensors receivingthe light of the light sources 21, 31. If the monitor receivers detectdeviations, readjustment is effected.

Besides the described embodiments, diverse variations are conceivable.In particular, the arrangement of the sensors and/or light sources canbe changed.

Likewise, further optical systems such as lenses can be provided at theplace of the filters 22, 23, 32 and 33 in addition to or instead of thefilters 22, 23, 32 and 33, for example to obtain a special focusing atthe place 15 or the sensors.

Further changes result from the use of several sensors 20, 30 andassociated light sources 21, 31 to permit measurements to be carried outin several tracks. One can also provide so many adjacent or overlappingtracks here to permit an all-over check of the bank note.

A further variation is possible if the light sources 21 or 31 emit notonly light below or above 400 nm, but light of a limited spectral range.The first light source 21 can e.g. emit light in a range of 350-400 nm,while the further light source 31 emits light in a range of 400-450 nm.In this case the sensors 20 or 30 and/or the filters 22, 23, 32, 33 canbe adapted accordingly.

In a further preferred embodiment of the inventive apparatus, a lock-inamplifier is provided for amplifying output signals, before theanalog/digital conversion thereof, at least one of the sensors 20, 30.Lock-in amplifiers are used in the measurement and processing of veryweak analog signals, whereby the signal background is suppressed verystrongly. With a lock-in amplifier the modulated output signal of asensor is amplified and demodulated in a synchronous detector with anormalized reference signal of the same modulating frequency. In alowpass the high-frequency components are then filtered out. The resultobtained is a signal which is proportional to the amplitude of theamplified emitted fluorescent light (sensor 30) or the reflectedultraviolet light (sensor 20). Since the use of a lock-in amplifier issuitable in particular for amplifying very weak [text missing—TheTranslator], it can measure very weak light with high precision. This isof advantage particularly when the intensity of the light sourcediminishes in the course of its service life and consequently thefluorescent light excited in the bank note to be checked or theultraviolet light transmitted becomes weaker.

The present invention is especially suitable for bank note processingmachines, e.g. for sorting and/or counting machines and/or moneyaccepting machines.

1. A method for checking the authenticity of sheet material, inparticular bank notes, by means of ultraviolet light, wherein the sheetmaterial is illuminated with ultraviolet light and the ultraviolet lighttransmitted by the sheet material is evaluated for checking theauthenticity of the sheet material.
 2. A method according to claim 1,wherein at least one threshold value or at least one pattern for thetransmitted ultraviolet light is derived from at least one authenticpiece of sheet material for checking the authenticity of the sheetmaterial.
 3. A method according to claim 1, wherein it is checkedwhether the ultraviolet light is converted by the sheet material tolight of another wavelength.
 4. A method for checking the authenticityof sheet material, in particular bank notes, by means of ultravioletlight, wherein the sheet material is illuminated with ultraviolet lightand a second light with a wavelength different from the ultravioletlight, and the ultraviolet light transmitted by the sheet material andthe second light transmitted by the sheet material are set in a mutualrelation, and the relation is evaluated for checking the authenticity ofthe sheet material.
 5. A method according to claim 4, wherein at leastone threshold value or at least one pattern for the relation is derivedfrom at least one authentic piece of sheet material for checking theauthenticity of the sheet material.
 6. A method according to claim 4,wherein the transmitted ultraviolet light and the transmitted secondlight come from the same place on the sheet material to be checked.
 7. Amethod according to claim 4, wherein the transmitted ultraviolet lightand the transmitted second light are evaluated at the same time.
 8. Amethod according to claim 4, wherein it is checked whether theultraviolet light is converted by the sheet material to light of anotherwavelength.
 9. An apparatus for checking the authenticity of sheetmaterial, in particular bank notes, by means of ultraviolet light,having a light source (21) for producing the ultraviolet light, wherebythe light source (21) illuminates the sheet material (BN) withultraviolet light, and a sensor (20) which produces values forultraviolet light transmitted by the sheet material (BN), and anevaluation unit (10) for checking the authenticity of the sheet material(BN) on the basis of the values of the sensor (20).
 10. An apparatusaccording to claim 9, wherein several sensors (20) and/or light sources(21) are present for detecting several tracks of the sheet material. 11.An apparatus according to claim 10, wherein the sensors (20) detect thesurface of the sheet material completely.
 12. An apparatus according toclaim 9, wherein a memory (11) is connected to the evaluation unit (10)and contains at least one threshold value or at least one pattern whichare derived from at least one authentic piece of sheet material forchecking the authenticity of the sheet material, and are compared by theevaluation unit (10) with the values or the sensor or sensors (20). 13.An apparatus according to claim 9, wherein at least one further sensor(30) is present whose values are checked by the evaluation unit (10) asto whether the ultraviolet light is converted by the sheet material tolight of another wavelength.
 14. An apparatus according to claim 9,wherein a lock-in amplifier amplifies the signal of at least one of thefirst sensor or sensors (20) and the further sensor or sensors (30). 15.An apparatus for checking the authenticity of sheet material, inparticular bank notes, by means of ultraviolet light, having a firstlight source (21) for producing the ultraviolet light, whereby the lightsource (21) illuminates the sheet material (BN) with ultraviolet light,and a first sensor (20) which produces values for light of the firstlight source (21) transmitted by the sheet material (BN), a second lightsource (31) for producing light with a different wavelength from theultraviolet light of the first light source (21), and a second sensor(30) which produces values for light of the second light source (31)transmitted by the sheet material (BN), and an evaluation unit (10) forchecking the authenticity of the sheet material (BN) on the basis of arelation of the values of the first sensor (20) to the values of thesecond sensor (30).
 16. An apparatus according to claim 15, wherein thesensors (20, 30) detect the same place (15) on the sheet material. 17.An apparatus according to claim 15, wherein the sensors (20, 30) detectthe sheet material at the same time.
 18. An apparatus according to claim15, wherein several sensors (20, 30) and/or light sources (21, 31) arepresent for detecting several tracks of the sheet material.
 19. Anapparatus according to claim 18, wherein the sensors (20, 30) detect thesurface of the sheet material completely.
 20. An apparatus according toclaim 15, wherein a memory (11) is connected to the evaluation unit (10)and contains at least one threshold value or at least one pattern whichare derived from at least one authentic piece of sheet material forchecking the authenticity of the sheet material, and are compared by theevaluation unit (10) with the relation of the values of the sensor orsensors (20) to the values of the second sensor or sensors (30).
 21. Anapparatus according to claim 15, wherein the evaluation unit (10) checksthe values of the second sensor or sensors (30) as to whether theultraviolet light is converted by the sheet material to light of anotherwavelength.